Hearing on US Weather and
Environmental Satellites: Ready for the
21st Century

­­­Introduction

I thank Chairman Inouye, Vice Chairman
Stevens, and the other Members of the Committee
for the opportunity to speak with you today on
the importance of observations in reducing the
impacts of hurricanes. My name is Greg J.
Holland and I am Director of the Mesoscale and
Microscale Meteorology Division in the Earth Sun
Systems Laboratory at the National Center for
Atmospheric Research (NCAR) in Boulder,
Colorado. I commenced my career as a weather
forecaster and my personal research has centered
on severe weather, especially hurricanes, and
has covered all aspects: basic theory; conduct
of major field programs; development of new
observing systems; computer modeling and direct
operational applications. I have authored or
co-authored more than 110 peer-reviewed
scientific journal articles and book chapters. I
have given several hundred invited talks
worldwide, as well as many contributed
presentations at national and international
conferences on hurricanes and related. I have
convened several national and international
workshops, and I have served on several national
and international science-planning efforts,
including Chairmanship of the World
Meteorological Organization’s Tropical
Meteorology Research Program. Currently, I am
serving on the National Research Council Study
Committee: New Orleans Hurricane Protection and
I am a Lead author on the U.S. Climate Change
Science Program (CCSP) Draft Synthesis and
Assessment Product 3.3: Weather and Climate
Extremes in a Changing Climate.

The work in my division at NCAR (www.mmm.ucar.edu/index.php)
includes research on the modeling and prediction
of hurricanes. We developed and are
continuously improving the Advanced Weather
Research and Forecasting (WRF) Model, which is
in widespread use for both research and
operations in over 70 countries. Our scientists
have lead the development of innovative
observing systems extending from specialized
field instruments to the Constellation Observing
System for Meteorology, Ionosphere and Climate
(COSMIC) satellite system, an innovative and
inexpensive system to obtain very accurate
vertical profiles of temperature and water vapor
in the global atmosphere for use in weather
forecasting. And we are currently collaborating
with the climate community on bringing the best
of weather and climate models together into a
system capable of analysis and prediction across
all time and space scales.

The U.S. has never been more vulnerable to
hurricanes and the scientific community is of
the strong and considered view that this
vulnerability will not decrease in the medium
term. A warming climate also may well
create more and more intense hurricanes,
although this is not certain. Accurate forecasts
and warnings of hurricanes are therefore a
national priority. I urge that the
Committee give the highest priority to the
passage of the National Hurricane Research
Initiative (NHRI), as this presents an
excellent, well-considered plan for improving
hurricane forecasting through the entire chain
from observations to warnings and reducing the
impacts of these dangerous storms.

Background Considerations

US Hurricane Responsibility
Regions

As shown in the accompanying figure from
the Interagency Strategic Research Plan for
Tropical Cyclones: The Way Ahead (ISRP), US
facilities have responsibility for forecasting
in all parts of the globe affected by
hurricanes. The NOAA Tropical Prediction
Center/National Hurricane Center (NHC) has sole
responsibility for the North Atlantic and
eastern North Pacific Basins. The NOAA Central
Pacific Hurricane Center (CPHC) has similar
responsibilities for the central North Pacific
region. The remainder of the hurricane globe is
routinely monitored and warned by the DOD Joint
Typhoon Warning Center (JTWC). While this is
done primarily for DOD interests, JTWC forecasts
are also included in the suite of advices used
by other domestic forecast services, and by
commercial services for both mobile and fixed
assets around the world. Thus the United
States has global responsibilities for
forecasting hurricanes.

This global responsibility has important
implications for our observational priorities in
support of hurricane forecasting. Satellite
observations are the foundation for our present
global observing system. Certain regions, such
as the eastern Pacific and North Atlantic have
the additional very substantial advantage of
aircraft reconnaissance. As you are well aware,
the U.S. satellite system, as described by the
recent National Research Council Report Earth
Science Applications from Space: National
Imperatives for the Next Decade and Beyond,
“is at risk of collapse.” Since accurate
forecasts of hurricanes beyond a day or so
depend upon global observations, this
degradation of the satellite system has
significant implications for the accuracy of
future hurricane forecasts, at a time when the
U.S. has never been so vulnerable.

Forecast System
Requirements

Hurricane observing and forecast
requirements are defined by the major offshore,
coastal and inland impacts:

Offshore, hurricanes impact high-seas
shipping and oil and gas rigs through high
winds, waves and ocean currents, including those
in the deep ocean. The forecast requirements
therefore focus on the future track, the
intensity, the overall wind structure, and the
oceanic response to its passage;

On approaching a coast, the scale of
hurricanes impacts rise sharply and now include
communities and commercial facilities, local
ecosystems, and port facilities. In addition to
the high winds, waves and ocean currents undergo
complex interactions in a variable coastline to
generate storm surges that can exceed 30 ft, be
accompanied by large waves and remove
substantial barrier islands. Flooding and
potential for landslip add to the concerns.
Forecasts therefore now also must include
details of the rain structure, including that
occurring in outer rainbands and the amplifying
effect of orography.

As a hurricane proceeds inland its high
winds diminish rapidly, but this does not
completely remove the danger. Now the impacts
largely arise from heavy rain and flooding, with
high-winds associated with squalls and tornadoes
also bringing the potential for local
devastation.

The forecast lead times vary according to
the time taken to effectively respond to the
approaching threat. Most coastal communities
require 48 hours notice of the onset of high
winds (which can be many hours before the
arrival of the hurricane core), some require 72
hours. Major port and offshore facilities can
require up to 4-5 days to prepare for a
hurricane passage. For this reason, NHC
forecasts were extended to 5 days in 2001.
Accurate forecasts at this extended time period
are dependent on the global observing system,
which again emphasizes the importance of
maintaining and improving satellite observing
systems.

These long lead times place great stress on
the forecast system to anticipate sudden or
sharp changes in hurricane characteristics,
especially near vulnerable communities and
facilities. The former Director of the Hurricane
Center Max Mayfield was quite clear in stating
that the nightmare scenario was un-forecast
rapid intensification or decay on approaching
the coast. Rapid intensification leaves
communities poorly prepared for a major
catastrophe, whereas rapid decay can lead to a
false sense of security and lack of adequate
response the next time a threat is
forecast.

Data Usage

Both the global and local data that are
collected are used in two major ways. A subset
is passed directly to the relevant hurricane
warning center, where they are used to analyze
current details of the storm, such as its
intensity, size, current track, etc. The warning
center also produces local statistical forecasts
of parameters such as track and intensity. The
full data set is fed into the computer
forecasting system where the relevant data are
assimilated into the suite of models that
produce both short and extended range hurricane
forecasts.

Thus, the observing system is one component
of a complex forecasting and warning process.
This entire process must be taken into account
when considering changes to the observing
system, as changes at one end often require
changes throughout the process to be fully
effective. This system also best operates in a
dynamic fashion, one where mobile resources
(such as aircraft) can be redeployed on the fly
to cover deficiencies or uncertainties that
appear in the forecast model calculations.

Current Deficiencies in the Forecast
System

There is no doubt that the quality of the
forecast can never be better than the
observations that are used to develop it.
However, before focusing on the observations
several deficiencies in the rest of the forecast
system require consideration. Hurricane track
forecasts and warnings have been improving
rapidly over the past 25 years due to (1)
improved global observations from
satellites, especially satellite atmospheric
temperature and water vapor sounders, (2)
improved computer models, (3) improved methods
of assimilating the many observations into the
models, and (4) improved understanding of
physical processes for inclusion in the
models. These improvements have
undoubtedly saved hundreds of thousands of lives
and billions of dollars of property.
However, our experience here shows that all four
components need additional attention and support
in order for us to arrive at the desired outcome
of increasing the accuracy of forecasts and
warnings. Forecasts of hurricane intensity
have shown less improvement, but there are good
scientific reasons for hope.

Our current approaches to assimilating the
data into the forecast models are not up to
international standards, especially for
intensity and structure forecasts. Important
data, such as land-based and aircraft radar, are
not used. The assimilation occurs by collecting
all data over a time period into a single
snapshot rather than being incorporated at the
time they are collected. This deficiency is
well-recognized and is being addressed in NCAR
and the Joint Center for Satellite Data
Assimilation. But the national investments do
not match the importance of this effort.
Assimilation research and application is
relatively inexpensive compared to the cost of
new observing systems, and it is important that
adequate and stable funding be maintained for
this work. A good working model should be
that ~15% of all observing system budgets be
devoted to ensuring the data are optimally used
in the forecast models by both observing system
sampling strategies and improved data
assimilation.

Current operational forecast models and the
computing facilities that they run on are simply
not adequate for intensity and hurricane wind
and rain structure forecasting, as emphasized by
the report of the recent NOAA Science Board
Hurricane Intensity Research Working Group
(HIRWG). Research results and experimental
forecast trials over the past few years have
clearly demonstrated this. An example is shown
in the accompanying figure (from S. Chen
University of Miami). In the top left is a radar
observation for hurricane Floyd (1999). The
other panels (in clockwise order) are forecast
precipitation patterns obtained from a
high-definition (1.6 km) research model, from
the typical resolution used by current hurricane
models (15 km), and from current global
operational models (45 km). The top right-hand
corner of each panel shows the scale of the
model grids relative to the hurricane. Clearly
the lower resolution models are incapable of
predicting critical details in the hurricane
core region. The required computer power
increases by 5-10 times for each halving of the
grid resolution, so this requires a substantial
investment in computing. But there are clever
ways of reducing this. Moving to fine definition
also requires an investment in applied research
to further develop the manner in which air-sea
interactions and the internal workings of clouds
are incorporated. Clearly, investing in
improved computer models and hardware is an
investment that has to be made if we are to make
substantive progress on predicting hurricane
intensity and structure.

The Observing System

A full analysis of the observing system is
beyond this brief testimony, so I will
concentrate on several areas of greatest need
and potential return for the investment for both
research and operational requirements. I will
also mention promising new observing systems
that are in need of research investigations for
potential future use. This analysis assumes that
the current suite of operational systems will be
retained. In particular the geostationary
satellite coverage and the aircraft
reconnaissance programs are essential for
maintaining the quality of analysis and
short-term forecasting of hurricanes, whereas
the entire satellite program including polar
orbiters contributes substantially to the
longer-term forecasts that are critical to
planning and response.

In my opinion, the areas of greatest need
and potential return are for satellite
observations of:

The full structure of the surrounding
atmosphere, including winds, moisture and
temperature;

The available ocean energy for hurricane
development, including the manner in which
hurricanes extract this energy from the ocean;

The surface wind structure and particularly
the extent of destructive winds in hurricanes.

Full Structure of the Surrounding
Atmosphere

Forecasts of hurricanes beyond about a day
relay heavily on numerical models of the
atmosphere. These models in turn are
dependent upon accurate measurements of
atmospheric temperatures, winds, pressure and
water vapor, not only in the immediate vicinity
of the hurricane, but over the much larger
environment of the storms, which extends
thousands of miles in all direction from the
hurricane center. The only feasible way of
obtaining these global observations is from
satellites, although weather balloons, aircraft
and surface-based observations make significant
contributions. The U.S. has been the world
leader in providing the satellites in both
geostationary and polar orbits that contribute
the vital data needed by the forecast
models.

However, as has been documented by the NRC
Decadal Survey and other reports and
testimonies, the U.S. satellite system is
in serious trouble---problems that threaten the
number and quality of atmospheric and ocean data
needed by the forecast models. For
example, the future planned polar-orbiting
NPOESS system has been reduced from six
satellites to four and from three orbits to
two. The NPOESS atmospheric sounding
system has been degraded, and the ocean
altimeter removed. In addition to this
degradation of the NPOESS sounding capability,
the planned Hyperspectral Environmental Sensor
(HES) has been removed from the next
geostationary satellite, GOES-R. Thus the
Decadal Survey recommended that NOAA develop a
strategy to restore the planned capability to
make high temporal and vertical-resolution
soundings from geosynchronous orbit.

Currently, atmospheric wind observations
from satellite are obtained by measuring the
movement of clouds and water vapor elements.
These have been a considerable boon to
forecasting in general, but they lack vertical
detail and are not obtainable in areas where
high cloud obscures the lower levels. I
support the NRC Decadal Survey recommendation
that NASA launch and test a lidar wind observing
system from space to test the ability to provide
comprehensive wind observations for the
globe---such wind measurements would be expected
to have a significant positive effect on
hurricane forecasts.

There is a new, exciting technique to make
atmospheric soundings of temperature and water
vapor from space at a relatively low cost of
approximately $3 per sounding. The new
technique called radio occultation, or RO, uses
the global GPS satellite signals to obtain
highly accurate vertical profiles of temperature
and water vapor in both cloudy and clear
regions, at a very low price compared to other
observing systems. In an ongoing
proof-of-operational-concept mission, COSMIC, RO
data have been shown to have a positive impact
on hurricane forecasting. The potential sounding
coverage of a full system over the North
Atlantic hurricane basin is shown in the
accompanying figure. For these, and a
number of other reasons, the recent NRC Decadal
Survey has recommended that NOAA implement an
operational constellation of RO satellites
beginning towards the end of the present
research COSMIC mission, in 2010 or 2011. RO
data are also very useful climate benchmark data
and contribute to space weather. As
recommended by the NRC decadal Study, NOAA
should begin planning for this operational
constellation immediately, while ensuring that
the COSMIC mission is continued for as long as
the satellites are producing good
data.

Ocean Energy

The available ocean energy dictates how
intense a hurricane can become. As hurricanes
move across changes in this ocean energy they
can rapidly intensify or decay and this can be
poorly forecast if we have not adequately
observed such changes. The observing system must
be able to include subsurface conditions, as
hurricanes extract energy from below the ocean
surface and can mix cold-subsurface water up to
the surface. A good example was provided by
Hurricane Katrina, as shown in the accompanying
figure (from ISRP). A deep warm pool of water
associated with the Gulf Stream Loop Current
(right panel) was completely hidden below
generally uniform sea surface temperatures (left
panel). Katrina developed rapidly on moving over
this deep warm pool then weakened substantially
as it moved towards the coast.

Oceanic instruments previously deployed to
drift over long periods or expendable
bathythermographs targeted to the expected
hurricane track by hurricane aircraft provide
one important means of observing this structure.
But these can only be applied locally and in
special circumstances and aircraft
reconnaissance is only available routinely the
North Atlantic and eastern North Pacific, with
special missions to the Central Pacific. A much
more robust and generally applicable approach is
to utilize satellite radar altimetry
observations. Because the warm water expands the
subsurface warm pools appear as local bulges in
the sea surface. Observations of these bulges
can be used in ocean models to provide a
definition of the subsurface structure that is
sufficient for hurricane forecasting.

The loss of the NPOESS altimeter in
recent cutbacks is a serious step backward for
observing such an important oceanic
feature.Satellite altimeter
measurements are a cost-effective method
obtaining critical information on the upper-
ocean energy storage and location of ocean
currents.

Surface Wind Structure

Surface wind observations from conventional
data, such as surface ships, are patchy and
often missing from the vicinity of hurricanes,
due the ships staying well clear. Such surface
wind data are important for several reasons: (1)
Locating and identifying the initial wind swirl
that indicates the development of a new
hurricane; (2) Correctly identifying the extent
of destructive winds, which is used to warn
shipping and emergency managers of the timing of
arrival of, for example, gale force winds (hese
winds may occur many hours before the
destructive core to substantially disrupt
preparations and evacuations); (3) assimilating
of the correct cyclone surface structure in
forecast models impacts the forecasts of track
and structure over the full forecast cycle. The
only way to obtain such information over the
global oceans is via satellite scatterometer
observations and the Sea Winds instrument on
QuickSCAT has demonstrated real skill in
improving hurricane track forecasts as
summarized by the IRSP. It is notable that this
improvement occurs mostly 2-3 days into the
forecast, which clearly indicates the importance
of the global nature of the QuickSCAT
observations.

Hurricane Reconnaissance

The requirements of an observing system are
varied. I have already indicated the importance
of global coverage by satellites, especially for
the longer-range hurricane forecasts. But these
global systems do not provide the depth of
detail, spatial density and time resolution
required in severe weather systems, such as
tropical cyclones. Indeed, it would be a waste
of resources to provide such coverage globally,
as in many cases it is simply not needed. These
data are best provided by adaptive and mobile
observing systems that can go to the system of
interest and take the required observations.

The U.S.A. has been fortunate to have had
routine aircraft reconnaissance in the North
Atlantic since soon after WWII. This
reconnaissance program has produced a
comprehensive long-period record of hurricane
structure and intensity that enables current
research in to the impacts of climate
variability and climate change on future risk.
It has also ensured the best possible forecast
and warning service at a cost that is a fraction
the direct savings. The reconnaissance system
has been steadily upgraded, with addition of new
platforms and instrumentation. Of particular
importance are: the Doppler radar capacity, and
particularly coordinated flight plans that
enable dual Doppler observations of the total
wind structure; GPS dropsondes that provide
detailed vertical structure, especially in the
poorly observed near ocean layer; and the
stepped frequency microwave radar (SFMR), which
provides excellent details of the core region
surface winds. The addition of the
G4 to the aircraft suite, together with GPS
dropsondes has provided near environmental
information that has demonstrably improved
forecast performance. I recommend in the
strongest possible terms that this aircraft
reconnaissance strategy be retained and further
upgraded. Initially upgrades should
concentrate not on new instrumentation, but on
more effective utilization of the data that are
currently collected, through effective
assimilation into computer models, and on the
design of new sampling strategies best suited to
support the evolving forecast requirement.

In recent times, adaptive approaches have
evolved in research mode to a stage where the
computer models are used to define where the
best data can be obtained, and the aircraft are
directed to obtain these data. An excellent
recent example of the effectiveness of this
approach in a research field experiment can be
seen in the recent NSF-sponsored Hurricane
Rainband Experiment (RAINEX).

The aircraft reconnaissance system is now
60 years old and based entirely on manned
aircraft. Recent developments with Unmanned
Aerial Vehicles (UAVs) and Underwater Autonomous
Vehicles (AUVs) have raised the potential for
substantial supplementation to the manned
aircraft approach. Advantages offered by UAVs is
the very long endurance and the capacity to take
observations in areas that are too dangerous for
manned aircraft and not able to be observed by
remote sensing. An example is the near surface
atmospheric layer. This is where the hurricane
gathers its energy and is the layer that
directly impacts coastal and offshore structures
through high winds, waves and storm surge. Yet
this is also the most under-observed part of the
hurricane. There is similar capacity and need
for AUVs to be targeted to areas of prime
interest for oceanic observations. Such capacity
would complement very nicely the operational
satellites and drifting or specially deployed
buoys. I do caution that care are needs to be
taken here as some UAV systems cost
substantially more than equivalent manned
aircraft and this additional cost would need to
be justified in terms of the expected forecast
improvements.

I fully support the recommendations
of an Interagency workshop on UASs, sponsored by
NOAA, NASA, and the DOE and held in Las Vegas,
Nevada, in February 2006, that an initial
demonstration should be conducted for low-level
observations, by a UAV in a hurricane.
The objective of the demonstration should be to
obtain detailed observations of the near-surface
tropical cyclone boundary layer environment and
to provide information on key questions of
whether such observations could: supply data
that will improve tropical cyclone intensity
forecasts; help improve our understanding of the
rarely observed tropical cyclone boundary layer
environment; and provide information that
successfully fills gaps in the current observing
system.

Conclusion

The nation has entered a difficult and
dangerous period of vulnerability to hurricane
impacts arising from a combination of sustained
enhanced hurricane activity and increasing
development in coastal regions. We must respond
and I thank the Committee for taking your
valuable time to consider an important part of
this required response. Satellites are a
mainstay of the hurricane forecast process. But
this process extends well beyond the taking of
observations and other areas are also in need of
serious consideration. In my testimony I
considered observing systems within the overall
hurricane forecasting and warning process. I
have identified several areas that should be
given priority attention:

Data Assimilation and Sampling
Strategies: Every new instrument should
be matched with an appropriate level of support
for ensuring the data enter the forecast process
in an optimal manner. A good working model
should be that ~15% of all observing system
budgets be devoted to both observing system
sampling strategies and improved data
assimilation;

Computer Modeling Capacity:
Without sufficient resources to improve the
resolution of hurricane forecast models and
their capacity to handle cloud-scale and air-sea
interaction processes, our capacity to advance
the forecasting of intensity and structure will
be severely limited;

Satellite Observing Systems: I
have identified three specific priority
areas: Lidar measurements of the complete
structure of atmospheric winds; Use of GPS Radio
Occultation to provide comprehensive atmospheric
temperature and moisture observations; Radar
altimetry to provide information on the ocean
heat energy storage that is available for
hurricane intensification; Scatterometer
observations of the surface winds to improve
location and structure information on hurricanes
and to improve longer range forecasts.

Aircraft Reconnaissance: I
have stressed the importance of this to the
National warning service and have noted several
instruments that have been of immense worth in
improving forecasts. I also have noted the
promising potential of new approaches using UAVs
and AUVs to monitor hitherto unobservable
components of the hurricane.

Of greatest priority in my view is for
there to be a coordinated, well-funded research
and system development approach focused on
reducing the impacts of hurricanes on vulnerable
communities. The review committees that were
formed after the disastrous 2005 hurricane
season have gathered views and information
widely and across all components of the
research, operational, engineering, social
science and emergency management community.
While there are differences of detail, these
groups have been unanimous in their call for
urgent action and in the general thrust of the
actions that are required. These are embodied in
the National Hurricane Research Initiative that
is before you for consideration. History has
shown that a full partnership between academia
and operations with adequate funding will result
in substantial forecast advances, including
identification of critical observing needs. I
urge you to give this urgent and serious
attention.

Thank you for the opportunity to address
the Committee on the importance of hurricane
observations as part of a complete forecast and
warning process – a topic that is has taken on
increasing urgency as the impacts of hurricanes
on our vulnerable communities is
rising.

* Any opinions, findings,
conclusions, or recommendations expressed in
this publication are those of the author and do
not necessarily reflect those of the National
Science Foundation.

** The National Center for
Atmospheric Research (NCAR) is sponsored by the
National Science Foundation.